This product is amazing. Other reviews say its bad in built up areas but they clearly have it set to a high station, set it to 88.00 and you will be fine. I have driven from city to city all over the Uk with this thing on and never had an interuption in a built up area due to being on a frequency no one seems to use!
Songs will be louder and quieter, due to the file on your actual computer and ipod. If you rip them at a low quality from a CD they will be quiet, if you download on itunes or from other sources then they are likely to either be very good or very poor.
I would highly recommend this product, and I work in electrical retail and have never had a single one returned for any of the reasons stated in the other reviews.